Hair cells, the primary receptors of the vertebrate auditory, vestibular, and lateral-line systems, transduce mechanical stimuli into electrical signals. The experiments detailed in this proposal involve the use of cell biological techniques to study how transduction takes place. The sensory macula of the bullfrog's sacculus will be maintained in vitro in media of defined compositions resembling those of endolymph and perilymph. Intracellular recordings will be made from individual hair cells while mechanical stimuli are applied directly to their hair bundles with fine glass probes. Voltage-clamp circuitry will be employed in order to measure the membrane conductance of hair cells and its dependence upon hair bundle position. The cations of the saline solution bathing the apical surfaces of the cells will be systematically replaced to determine the ionic dependence of the transduction process. Attempts will be made to microdissect the hair bundles of impaled cells so the stimuli may be applied selectively to kinocilia or stereocilia. Adaptation of the transducer to static mechanical displacements of the hair bundle will be sought. The latency of the hair cell's receptor potential and its temperature dependence will be measured by extracellular recordings of microphonic responses from preparations stimulated with very rapid mechanical displacements. The pathological effects of aminoglycoside antibiotics on the transduction process will be evaluated both by intracellular recording and by freeze-fracture electron microscopy. The action potential mechanism of hair cells will be studied to determine the membrane surface in which it lies and the ions it involves; this approach may indicate whether the spike is associated with the synaptic release process or with amplification of receptor potentials. The electrical relationship of hair cells with one another and with supporting cells will be studied by both coupling experiments and intercellular dye transfer.